This invention relates to improvements in cooling arrangements for rotating electrical machines. More particularly, the invention is concerned with the efficient cooling of such machines
The term xe2x80x9crotating electrical machinexe2x80x9d is intended to cover any form of apparatus having a rotating member which generates, converts, transforms or modifies electric power, inter alia, such machines will comprise motors, generators, synchronous condensers, synchronous converters, rotating amplifiers, phase modifiers and combinations of these in any one machine.
With increasing development of permanent magnets and the use of exotic materials in machines, it is now possible to produce relatively high power/high torque motors which occupy far less space than equivalent machines of, say, five years earlier. This reduction in size brings with it an increase in complexity in cooling the machines. Heat dissipation is also a problem with machines that do not employ permanent magnets. The more efficient the cooling, the higher the power density and hence smaller the machine that can be produced.
In a normal arrangement, it is known to provide a laminated component which forms a part of the stator of the machine. This is typically formed from stacks of sheets of electrical grade steel which are often provided with insulating coatings. Each sheet may, for example, be of generally disc or annular form.
Between stacks of the sheets are often provided passageways for cooling fluid, e.g. air, which passageways extend substantially radially. More particularly, in a typical machine the radial inner or outer ends of the passageways will adjoin with the air gap between the rotor and stator. Our published patent document GB 2 338 350 A discusses how to define such passageways more advantageously in terms of the cooling effect they can produce.
Whilst such an arrangement allows the passage of cooling fluid from the inside to the outside (or from the outside to the inside) of the rotor or stator, it has been found that the cooling effect that is provided is insufficiently controlled to produce even cooling over the entire circumferential and axial extent of the rotor or stator. In an electrical rotating machine even cooling is essential in order to avoid localised overheating of windings, thus enabling increased power densities to be obtained.
It is an object of the present invention to provide an arrangement whereby a more controlled cooling of the machine can be achieved.
Accordingly, the invention provides an electrical machine comprising a stator and a rotor, with a gap defined between the stator and the rotor, the machine further comprising;
coolant supply duct means and coolant exhaust duct means,
a plurality of substantially radially extending coolant passageways provided in a laminated core section of at least one of the stator and the rotor, the coolant passageways being defined between axially spaced stacks of laminations in the laminated core section, the radial passageways being connected to the coolant supply duct means via the gap between the stator and thd rotor, and
a matrix of coolant duct sections extending circumferentially and axially of the laminated core Section, a plurality of adjacent coolant duct sections being in fluid communication with each other transverse of the radial direction to transfer coolant in predetermined paths within the coolant duct matrix, the matrix having first and second radially spaced apart faces, the first face being in fluid communication with the radially extending coolant passageways in the laminated core section, characterised in that the second face is in fluid communication with the coolant exhaust duct means, such that selected of the coolant duct sections communicate directly with the coolant exhaust duct means through the second face of the matrix.
In one possible arrangement of the machine, the first and second radially spaced apart faces of the matrix of coolant duct sections comprises its radially inner and outer faces respectively.
The matrix of coolant duct sections is conveniently defined between a plurality of annular side walls which extend radially and circumferentially of the laminated core section and a plurality of end walls which extend radially and axially of the laminated_core section, To facilitate the transfer of coolant in the predetermined path within the coolant duct matrix, apertures are provided in selected of the side walls and end walls of the coolant duct sections. The size and number of the apertures are preferably selected to achieve desired axial and circumferential pressure differences within the matrix of coolant duct sections. It is possible that each side wall and each end wall will have a respective aperture, but this will be determined by detailed design using computational flow analysis.
In a preferred embodiment of the invention in which the coolant duct sections are defined as above, a side wall at each axial end of the matrix constitutes an end plate of the laminated core section.
The end walls may be equi-angularly spaced around the laminated core section.
Preferably, each coolant duct section communicates directly with a plurality of the radially extending coolant passageways through the first face of the matrix.
Advantageously, the coolant supply duct means may define a coolant supply path directed towards an axial end of the laminated core section through a plenum chamber axially adjacent the laminated core section, the gap between the rotor and the stator communicating with the plenum chamber to provide a coolant flow path from the plenum chamber to the radially extending coolant passageways in the laminated core section. From a practical design point of view, it is preferable if the coolant supply duct means defines coolant supply paths directed towards both axial ends of the laminated core section through respective plenum chambers.
It is particularly advantageous for cooling end windings of the laminated core section if apertures in at least one of the end plates of the laminated core section provide a coolant flow path from the plenum chamber to selected of the coolant duct sections in the matrix, since the coolant can flow past the end windings on the way to the matrix.
The invention particularly facilitates designs in which at least one of the coolant supply duct means and the coolant exhaust duct means extends radially of the machine. This is useful where access to the machine is confined to certain angular positions around the machine.
The plurality of substantially radially extending coolant passageways provided in the laminated core section preferably comprise axially thin annular ducts. In accordance with our published patent document GB 2,338,350 A, the axially thin annular ducts can be defined by spacer means provided between adjacent confronting stacks of laminations in the laminated core section. The spacer means may thus comprise a pattern of mutually spaced apart axially projecting generally cylindrical members attached to at least one of the confronting laminations, the pattern extending between radially inner and outer peripheries of the confronting laminations. The pattern of generally cylindrical members may extend throughout the total annular extent of the passageway.
It should be noted that the matrix of coolant duct sections preferably extends around the entire circumference of the laminated core section.
It is convenient for layout of radially extending exhaust ducts if the coolant duct sections which communicate directly with the exhaust duct means comprise approximately half the circumferential extent of the matrix.
The invention further provides an electrical machine as described above, comprising a propulsion unit for a ship in which the machine is located within a bulbous portion extending from a hull of the ship, the rotor of the machine being located on a propeller shaft which extends outside the bulbous portion for propulsion of the ship, the coolant supply duct means and the coolant exhaust duct means being arranged within the bulbous portion to supply and exhaust coolant through the ship""s hull.
It will be understood that by radially extending coolant passageways provided in the laminated core section, we mean passageways along which fluid can move from a first radial position to a second radial position. This may be from the innermost to outermost perimeter of the stator or rotor, or vice-versa. During such movement in radial passageways designed in accordance with our prior published patent document GB 2,338,350 A, it is envisaged that a substantial circumferential movement will also occur, due to the relative rotation between the rotor and stator, but primarily due to the influence of the circumferential pressure differences developed within the matrix of cooling duct sections. The fluid may even have a greater circumferential velocity than radial velocity on moving through such radial passageways.
By providing a circumferential matrix of coolant duct sections around the laminated core of the rotor or stator it is possible to control the passage of fluid through the machine to optimise cooling of the rotor and/or stator in a predetermined manner. This is achieved at the design stage by computational design by varying the size of the openings between each adjacent duct section, thus allowing the cooling flows in the radial passageways to be optimised with respect to the losses in each duct section.
The openings in the walls of the duct sections, e.g., between adjacent duct sections or between the duct sections and the exhaust duct means, may be laser cut into the material. Of course, other cutting methods may be employed.
It will be appreciated that the coolant duct sections do not need to be fabricated from solid plates of material. Other fabrication techniques are envisaged within the scope of the present invention, for example, a honeycomb sandwich or expanded metal construction could be used to produce the dividing walls.
In a preferred arrangement, the machine includes a stator extending around the outside of a rotor, the stator having radial passageways and the matrix of coolant duct sections extending around the outside of the stator. In an alternative arrangement, the matrix may extend around the inside of the rotor with the rotor having radial cooling passageways and rotating within the stator. In yet a further arrangement, the rotor may rotate around the stator with the matrix being provided around the outside of the rotor.
The matrix of cooling duct sections may comprise an integral part of the laminated core section of the machine. It may alternatively form a sleeve which is adapted to be secured around the circumference of the laminated core section. This may or may not be removable in use.
The combination of the arrangement of the radial passageways and their cylindrical members and the apertures in the walls between the duct sections is preferably chosen to maintain a substantially uniform temperature throughout the machine during normal operation.
The provision of the duct sections and their interconnecting holes ensures that the cooling fluid can travel a significant circumferential distance between entering the machine and leaving the machine. This enables the coolant for the machine to be supplied and exhausted from any desired circumferential location on the machine ration.